1. Field of the Invention
The present invention relates to a fiber-reinforced metal composite (FRM) comprising reinforcing fibers and an aluminum alloy as a matrix.
2. Description of the Related Art
Recently, due to the superior strength and rigidity thereof, fiber-reinforced metal composites have been used for various machine parts and structural materials. Among these composites, a fiber-reinforced composite material of aluminum or an alloy thereof reinforced with inorganic fibers or metal fibers is light and has a high rigidity and high heat resistance. The inorganic fibers include, for example, continuous fibers such as Si--Ti--C--O fibers, SiC fibers, alumina fibers, boron fibers and carbon fibers, and short (staple) fibers, such as SiC whiskers, Si.sub.3 N.sub.4 whiskers and alumina whiskers. The aluminum or alloy thereof of the matrix is generally a standard product meeting the requirements of Japanese Industrial Standards (JIS), such as 1070 (pure aluminum), 6061 (Al--Mg--Si series), 2024 (Al--Cu--Mg series), and AC4C (corresponding to A356.0 of the Aluminum Association (AA)), or the like. Heretofore, such fiber-reinforced metal composites have been produced by methods such as infiltration, diffusion-bonding, and pressure casting.
In general, reinforcing fibers are used at a volume percentage of from 40 to 60% in the fiber-reinforced metal composite produced by a pressure casting method, and thus inevitably the fibers come into contact with each other, and this contact between the fibers prevents the obtaining of the expected strength of the fiber-reinforced metal composite. Further, sometimes the compatibility between the reinforcing fibers and the metal matrix is poor and a reaction occurs at the interface, which causes a deterioration of the reinforcing fibers. Furthermore, in the case of a matrix of aluminum or an alloy thereof, in particular, undesirable brittle crystals are generated.
It is considered that pure aluminum is most suitable as the matrix metal, since deterioration of the fibers and generation of brittle crystals do not occur when pure aluminum is used. Nevertheless, since pure aluminum has low strength, when continuous reinforcing fibers are used, the fiber-reinforced aluminum composite has poor strength in a transverse direction at a right angle to the continuous fiber orientation, and if a component part is formed only partially of fiber-reinforced aluminum, and the remainder thereof does not contain the reinforcing fibers but is formed of aluminum alone, such a remaining part has low strength.
To solve the above-mentioned problems, composite materials (fiber-reinforced metal composites) of an aluminum alloy matrix have been proposed. For example, an aluminum alloy containing 0.5 to 6.0 wt% of nickel (Ni) is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-124245, and another aluminum alloy containing at least one element selected from the group consisting of Bi, Sb, Sn, In, Cd, Sr, Ba and Ra is disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-169034. Nevertheless, these proposed fiber-reinforced metal composites do not have the required strength or corrosion resistance.